We have the Power Board which is usually S.M.P.S but in old ones they used to have special types of transformer with many output to supply the power to the other circuit.
Next you have the Loader which houses the Pickup and then the Decoder (electronics board) all interconnected by use of wires (conductors) or ribbon connectors.
So let assume you have received a DVD from a customer with the No Disc error, first before opening up do some initial test. Open the drawer and load a Music Disc which you are sure it is not scratched or defectiveÖif the DVD open and closes the door fully then we can conclude that the doors are okay.
Then listen above the loader for the sound of disc spinning, the way the disc spins can tell you a lot if the spinning is healthy or not. The disc should spins smoothly at around 500 RPM if everything is okay.
Now open up the machine and go to the pickup, if the pickup is on the inner area push it slowly and carefully to the outer zone with power off.
Now power on the DVD and observe the pickup and the Lens. For safety precaution donít look at the lens directly with your eyes, just look at an angle from a distance.
If the pickup moves to the inner area smoothly and after reaching the inner lane the lens start moving up and down emitting red light then most probably the lens is okay.
If the disc is spinning slowly expect the spindle motor is probably shorted or the power supply to the spindle motor has some problem
To test the spindle motor with a DMM, set your meter to low resistance test (200 ohm) range, if it is okay should read between 5 and 20 ohms.
On analogue meter, this is my favorite set the meter to X1 and measure across the two wires coming from the motor(red and black) if the motor is okay, it will spins at very high speed indicating to you that it is up to the task.
If the spindle motor is healthy then follow the supply for this motor to the decoder(motherboard) looking for the filter capacitor for that line, usually 470uF/10v, this capacitor has a high failure rate and should be tested with ESR meter or directly replace it. If you find this capacitor has swollen top just replace it with the same value capacitor but high voltage rating (470uF/16V) is okay.
Sometimes also a no disc symptoms can be caused by disc table (spindle platter) height set too low or too high. If you spin the disc with your hand it should rotate freely.
In conclusion most of DVD problems are mechanical and very inexpensive to repair and doesnít require sophisticated machinery to test just observation using the best tools I have come to realize in my troubleshooting experience which are absolutely free, YOUR SET OF EYES.
A word of advice- I have found several of these spindle motors which are not working right from the shop and therefore I advise you to test on the counter before taking it home only to realize that itís not working. This is also true with other components make it a routine to test components before replacing them in circuit.
Thank you guys.